Delphi中的匿名方法Anonymous Methods in Delphi
一、定义
顾名思义，匿名方法是没有名称的过程或函数。匿名方法将代码块视为实体，可以将其分配给变量或用作方法的参数。此外，匿名方法可以引用变量并将值绑定到定义该方法的上下文中的变量。可以使用简单的语法定义和使用匿名方法。它们类似于其他语言中定义的闭包的构造。As the name suggests, an anonymous method is a procedure or function that does not have a name associated with it. An anonymous method treats a block of code as an entity that can be assigned to a variable or used as a parameter to a method. In addition, an anonymous method can refer to variables and bind values to the variables in the context in which the method is defined. Anonymous methods can be defined and used with simple syntax. They are similar to the construct of closures defined in other languages.
二、案例
unit AsyncTask;
interface
uses
System.SysUtils, System.Threading;
type
TAsyncBackgroundTask<T> = reference to function: T;
TAsyncSuccessCallback<T> = reference to procedure(
const TaskResult:T );
TAsyncErrorCallback = reference to procedure(
const E: Exception );
TAsyncDefaultErrorCallback = reference to procedure(
const E: Exception;
const ExptAddress: Pointer );
Async = class sealed
public
class function Run<T>
(
Task: TAsyncBackgroundTask<T>;
Success: TAsyncSuccessCallback<T>;
Error: TAsyncErrorCallback = nil
) :ITask;
end;
var
DefaultTaskErrorHandler: TAsyncDefaultErrorCallback = nil;
implementation
uses
System.Classes;
{ Async }
class function Async.Run<T>(
Task: TAsyncBackgroundTask<T>;
Success: TAsyncSuccessCallback<T>;
Error: TAsyncErrorCallback ) :ITask;
var
LRes: T;
begin
Result := TTask.Run(
procedure
var
Ex: Pointer;
ExceptionAddress: Pointer;
begin
Ex := nil;
try
LRes := Task(); //:1.后台任务的方法:返回泛型T
if Assigned(Success) then
//:如果指定了参数Success的类型及其参照reference
begin
TThread.Queue(nil, //:Queue在主线程(UI线程)中运行
procedure
begin
Success(LRes); //:2.队列化-后台任务的成功回调的函数:传入这个泛型T
end);
end;
except
Ex := AcquireExceptionObject;
//:请求系统返回异常对象:system.AcquireExceptionObject
ExceptionAddress := ExceptAddr;
//:请求系统返回异常地址:system.ExceptAddr
TThread.Queue(nil, //:Queue在主线程(UI线程)中运行
procedure
var
LCurrException: Exception;
//:系统异常类Exception实例变量
begin
LCurrException := Exception(Ex);
//:系统异常类获取某个异常对象
try
if Assigned(Error) then
Error(LCurrException)
//:3.1.队列化-后台任务的异常回调的函数:传入这个异常LCurrException
else
DefaultTaskErrorHandler(
LCurrException,
ExceptionAddress );
//:3.2.队列化-后台任务的默认异常回调的函数:传入这个异常LCurrException及其地址ExceptionAddress
finally
FreeAndNil(LCurrException);
end;
end);
end;
end);
end;
initialization
DefaultTaskErrorHandler :=
procedure(
const E: Exception;
const ExceptionAddress: Pointer )
begin
ShowException(E, ExceptionAddress);
end;
end.
三、匿名方法的定义
// Generic Anonymous method declarations //System.SysUtils;
//类：匿名方法的定义：
type
TProc = reference to procedure;
TProc<T> = reference to procedure (Arg1: T);
TProc<T1,T2> = reference to procedure (Arg1: T1; Arg2: T2);
TProc<T1,T2,T3> = reference to procedure (Arg1: T1; Arg2: T2; Arg3: T3);
TProc<T1,T2,T3,T4> = reference to procedure (Arg1: T1; Arg2: T2; Arg3: T3; Arg4: T4);
TFunc<TResult> = reference to function: TResult;
TFunc<T,TResult> = reference to function (Arg1: T): TResult;
TFunc<T1,T2,TResult> = reference to function (Arg1: T1; Arg2: T2): TResult;
TFunc<T1,T2,T3,TResult> = reference to function (Arg1: T1; Arg2: T2; Arg3: T3): TResult;
TFunc<T1,T2,T3,T4,TResult> = reference to function (Arg1: T1; Arg2: T2; Arg3: T3; Arg4: T4): TResult;
TPredicate<T> = reference to function (Arg1: T): Boolean; // Predicate : 匿名断言 （Assert (TPredicate<T>) ）
匿名方法：匿名过程 匿名函数 匿名断言
